Early detection is one of the most challenging issues in cancer diagnosis. Currently, diagnosis depends on a variety factors including illness symptoms, the detection of biomarkers in blood and/or body fluids, the microscopic analysis of biopsy samples, as well as imaging technology. Limited sensitivity in these methods and technologies can result in the delay of treatment. The National Cancer Institute has indicated there is an urgent need of new technologies for cancer early diagnosis.
Cancer is known as a disease driven by genetic abnormalities. Recently, however, research has suggested that epigenetic alterations of gene function may also be central to the pathogenesis of this disease. Epigenetic alterations include heritable changes in the gene expression that are not caused by direct alteration of the gene's nucleotide sequence. Abnormal DNA methylation at gene transcription sites can result in epigenetic silencing of genes that protect against tumor formation or that repair DNA. Research into gene silencing has focused on the regions of high CpG content, known as CpG islands. CpG islands are often located near gene transcription sites. In normal cells, most promoter-associated CpG islands are unmethylated. But in cancer cells, promoter region CpG islands are most likely to be methylated. Thus, the detection of promoter methylation in tumor suppress genes is one of most important assays in early cancer diagnosis. Conventional methods for DNA methylation detection use methylation specific and/or methylation sensitive restriction enzymes for restriction landmark analysis. Recently, several advanced methods have been developed for DNA methylation detection, including bisulfite sequencing, methylation-specific PCR, MethyLight, CpG island microarray. However, major drawback with these methods include complicated procedures, relatively low sensitivity, time consuming and false positive. Therefore, the development of new technologies to improve DNA methylation detection will have a significant impact in early cancer detection.
The p16INK promoter was chosen as a target of the detection model, since its protein inhibits cell cycle progression. Methylation of CpG islands in p16 promoter and the first exon regions inactivates transcription of the p16 gene. This is significantly associated with lung cancer. Recently, field effect transistor (FET) based electronic charge detectors were introduced into DNA detection by several research groups. However, using charge detector to report DNA methylation events is a challenge, since both methylated and unmethylated DNA carry the same amount of electrical charge. In light of the foregoing there is a need for a DNA methylation detection system that has increased sensitivity yet is relatively easy to operate and without the need for bisulfite treatment or PCR amplification.